<script>
// 연산자의 연산 우선순위
function getOpPrec(op) 
{ 
    switch (op)
    {
        case '*':
        case '/':
            return 5;
        case '+':
        case '-':
            return 3;    
        case '(': 
            return 1;    
    }

    return -1;
}

// 연산자의 우선순위 비교
function whoPrecOp(op1, op2) 
{
    return getOpPrec(op1) >= getOpPrec(op2);    // op1의 연산순위가 높거나 같다면 참
}

function postfixNotation(exp) 
{  
    var stack = [], convExp = [], tok, popOp; 
    exp = exp.replace(/\s/g, '').match(/[\d\.]+|[^\d\.]/g).reverse();  // 공백제거 및  배열로 분리

    while (tok = exp.pop()) {    
        // 숫자가 아니라면(연산자라면) 
        if (isNaN(tok)) {    
            switch (tok)
            {
                case '(':
                    stack.push(tok);
                    break;
                case ')':
                    while (1) {
                        popOp = stack.pop();
                        if ( popOp == '(' )
                            break;
                        convExp.push(popOp);
                    }
                    break;
                case '+': case '-':
                case '*': case '/':
                    while (stack.length && whoPrecOp(stack[stack.length-1], tok))
                        convExp.push(stack.pop());
                    stack.push(tok);
                    break;
            }
        } else     // 숫자라면(피연산자라면)
            convExp.push(tok); 
    }          
    while (stack.length)  
        convExp.push(stack.pop());    

    return convExp;  
}

function evalPostfixNotation(exp) 
{
    var i, tok, n1, n2, stack = [];
    for (i in exp) {   
        tok = exp[i];
        // 연산자라면 
        if (isNaN(tok)) {
            n2 = Number(stack.pop());
            n1 = Number(stack.pop());

            switch (tok)
            {
                case '*':
                    stack.push(n1 * n2);
                    break;
                case '/':
                    stack.push(n1 / n2);
                    break;
                case '+':
                    stack.push(n1 + n2);
                    break;
                case '-':
                    stack.push(n1 - n2);
                    break;
            }
        } else     // 숫자라면            
            stack.push(tok);
    } 
    return stack.pop();
}

document.write( evalPostfixNotation(postfixNotation( '((3.5 - 2) + 3.4) * (14 - 10)' )));
</script>